The field of this invention relates to liner hangers, and, more particularly, to the techniques for securing liner hangers in well bores.
Liner hangers are secured in the well bores by slips. Actuation systems for such slips in the past brave employed full circumference hydraulically actuated pistons to move the slips. These designs presented a pressure rating problem in that the full circumference piston frequently had a maximum working pressure significantly lower than the mandrel which it surrounded. Thus, this type of design limited the maximum working pressure in the string to the rating of the cylindrical piston housing assembly. For example, it was not unusual in prior designs to have mandrels rated for 12,000 PSI while the surrounding cylinder housing for the cylindrical piston to only have a rating of approximately 3,000 PSI. In an effort to improve the shortcoming of this design, another design illustrated in U.S. Pat. No. 5,417,288 was developed. In this design the mandrel body received a pair of bores straddling each of the slips. A piston assembly was mounted in each of the bores with all of the necessary seals. The application of hydraulic pressure in the mandrel into all the piston bores actuated the pistons on either side of each slip through a common sleeve to which all the slips were attached. This design, however, was expensive to manufacture and had many potential leak paths in the form of the ring seals on each of the pistons wherein each slip required two pistons. This design, however, did provide for a higher pressure rating for the liner hanger body. It also used the hydraulic pressure directly to actuate the slips. Necessarily it did not include a locking feature against premature slip movements due to inadvertently applied pressures. The design in the U.S. Pat. No. 5,417,288 also did not provide for flexibility for changed conditions down-hole which could require additional force to set the slips. In essence, each application was designed for a pre-existing set of conditions with field variability not included as a feature of that prior art design.
Slip assemblies in the past have been configured in a variety of ways. In one configuration, when the slips are actuated, the load is passed through the slips circumferentially through their guides or retainers and transmission of the load to the underlying mandrel is avoided. In other more traditional designs, the slips are driven along tapered surfaces of a supporting cone and the loading is placed on the supporting mandrel is in a radial direction toward its center, thus tending to deform the mandrel when setting the slips. Typical of such applications are U.S. Pat. Nos. 4,762,177, 4,711,326 and 5,086,845.
The design of the liner hanger needs to accommodate circulation of mud and cement. The prior designs, particularly those using a cylindrical piston, obstructed the passages that could have been used for circulating cement and mud.
The apparatus of the present invention has many objectives. A versatile actuation system for a locking system is provided. The apparatus uses a combination of hydraulic pressure to defeat a locking mechanism which in turn allows mechanical actuation of the slips. The slips are configured to pass the loading into the slip seat and then into the mandrel in a manner so as not to deform the mandrel. The slips act independently of each other and transfer their load through the surrounding slip seat directly to the mandrel. The slip seats are attached to the mandrel without welding because standard setting organizations and well operators have restrictions against connecting parts made of certain materials by welding or against welding altogether in down-hole tools. The slip seats are spaced from each other to provide flow channels along the exterior of the liner hanger to facilitate the movement of cement or mud. Those passages are continued for the length of the tool. The actuating piston assembly to defeat the lock mechanism is a bolt-on arrangement which can be readily interchanged in the field to react to changing down-hole conditions. The actuating piston is fully compensated for thermal effects and a system is provided to vent any gases from the piston actuation system which is used to defeat the lock. The lock can be in a number of alternative styles. One of which involves using a dog to hold the parts together for run in and liberating the dog from its groove to allow setting of the slips, which is preferably done by a plurality of springs. The parts are also disposed in a preferred spacing to make maximum use of the limited force available from the piston assembly for releasing the lock. The lock configuration can also be in the form of a split ring held together by a yoke which allows relative movement when the yoke is shifted, allowing the split ring to expand. These and other objectives of the present invention will become more apparent to those skilled in the art from a review of the preferred and alternative embodiments described below.
A liner hanger assembly has a slip actuation system which is locked for run-in. A piston assembly bolts onto the mandrel in a sealable manner to actuate a mechanical lock. Upon release of the lock, a plurality of springs actuate a sleeve which is in turn attached to the slips to move them relative to their slip seats. In an alternative embodiment, a plurality of springs can directly move the slips relative to their slip seats, when the springs are released. The slip seats are preferably mounted to the mandrel without welding and have longitudinal spaces for mud or cement flow therebetween. Load is distributed from each slip through its slip seat into the mandrel without interaction from an adjacent slip or slip seat. A rupture disk ensures that a predetermined pressure is built up before the piston can actuate to defeat the lock. The lock can come in a variety of configurations. One of which is a sliding sleeve over a dog and another is a yoke over a split ring which, when shifted, allows the split ring to expand, thus unlocking the parts. Yet another variant is a yoke restraining a split ring. The slips can also be configured to allow flow of mud or cement behind them, thus reducing the resistance to flow of such materials.